WO2001009229A1 - Method of producing antimicrobial synthetic bodies with improved long-term behavior - Google Patents

Abstract

The invention relates to a method of producing antimicrobial synthetic bodies, including shaping a preproduct. The inventive method is characterized in that at least one component of the preproduct is treated with a metal colloid before shaping.

Description

 Process for the production of antimicrobial plastic bodies with improved long-term behavior

The invention relates to processes for the production of antimicrobial metal-containing plastic bodies, in particular articles for medical use. These objects are used in particular in the form of catheters.

A significant disadvantage of plastic objects for medical needs, especially short and long-term catheters, is the fact that the plastics used can be easily populated with often multi-resistant germs, which on the surface of the plastic body or on the inside and outside of the catheter Form biofilm. Prophylactic impregnation of the surfaces with antibiotics is ruled out because of the high selection of resistant microorganisms involved.

Numerous attempts have therefore been made in recent years to coat the plastic surfaces with silver ions, e.g. originate from silver nitrate, acetate, chloride. Of all heavy metal ions, silver ions have a very broad anti-microbial spectrum and a high toxicity to microorganisms due to e.g. binding to the cell wall via SH groups, blocking of the respiratory chain, prevention of cell proliferation by DNA binding, but low toxicity to animal cells. However, sufficient microbial activity could not be observed in various clinical studies. In addition, the caustic effect or poor water solubility of silver salts leads to further problems in use.

When metal surfaces such as silver come into contact with physiological NaCl solution, metal ions (silver ions) are released depending on the size of the metal surface. However, the addition of metal powder, for example silver powder, to a polymer, for example polyurethane, does not lead to success, since relatively high concentrations of metal powder are required due to the small surface area, which is causes mechanical problems in the plastic material. The critical surface required for antimicrobial effectiveness can therefore not be achieved by adding metal powder.

EP-A-0 71 1 113 discloses a new technology in which metallic silver is evaporated on polyurethane foils and these are compounded in comminuted form. This made it possible to achieve a uniform distribution of silver particles in the polymer material and thus to achieve a surface that was sufficiently large for bacteriostatic activity. The antimicrobial effectiveness of these plastic bodies has been well documented in terms of reducing and preventing adherence, biofilm formation and long-term behavior, as well as toxicity and tolerance. However, the applicability of the above plastic bodies is limited by a time-consuming and cost-intensive manufacturing process, especially caused by the vapor deposition with silver.

Furthermore, TJS-A-5, 180,585 describes an antimicrobial composition comprising inorganic particles with a first microbicidal layer and a second layer for protecting the underlying first layer. The manufacturing process is relatively complex.

The object of the present invention is therefore to provide a process for the production of antimicrobially active plastic bodies which do not have the above disadvantages, i.e. are easy to manufacture and provide a sufficient silver ion concentration on the surface.

This object is achieved by a method which is characterized in that at least one component of the preliminary product of the molded body is treated with a silver colloid before the plastic body is molded.

Many polymeric compounds that are commonly used in the medical field come into consideration as the starting material for the plastic body. These are in particular polyethylene, polypropylene, cross-linked polysiloxanes, polyurethanes, polymers based on (meth) acrylate, cellulose and cellulose derivatives, polycarbonates, ABS, tetrafluoroethylene polymers and polyethylene terephthalates, as well as the corresponding copolymers. Polyurethane, polyethylene and polypropylene and polyethylene-polypropylene copolymers are particularly preferred. The metal used is preferably silver, copper, gold, zinc or cerium. Of these metals, silver is particularly preferred.

In addition to the colloidal metal, one or more polymer materials are used in the production of the plastic bodies according to the invention. Other additives can also be added to the mixture of colloidal metal and plastics). These are, in particular, inorganic particles such as barium sulfate, calcium sulfate, strontium sulfate, titanium oxide, aluminum oxide, silicon oxide, zeolites, mica, talc, kaolin, etc. Barium sulfate, which can simultaneously serve as an X-ray contrast agent for special applications, is particularly preferred.

Before forming, one or more polymer components are treated with the colloidal metal solution and / or one or more of the inorganic additives.

After mixing the (partially) treated with a colloidal metal

Starting materials, the mixture obtained is processed to a

Obtain plastic molding. This can be done in mixers, kneaders, extruders, injection molding machines or (hot) presses.

The metal colloids with which the plastics or inorganic particles are treated are suitably produced by reducing metal salt solutions. Protective substances such as gelatin, silica or starch can be used to stabilize the resulting colloid.

In the case of the preferred metal silver, for example ammoniacal silver nitrate solution in the gelatin is slowly mixed with a suitable reducing agent. In addition to aldehydes (eg acetaldehyde), aldoses (eg glucose), quinones (eg hydroquinone), inorganic complex hydrides (sodium or Potassium boranate), reducing nitrogen compounds (hydrazine, polyethyleneimine) and ascorbic acid.

Plastic intermediate products, such as Pellets, and / or the inorganic particles, e.g. Barium sulfate are then treated with this colloidal silver solution, dried and brought into the appropriate form. The application of the silver colloid to the starting materials and the subsequent drying can be repeated several times, so that very high silver concentrations can be introduced into the plastic material in this way. This is particularly advantageous for the silver coating of barium sulfate, since prior coating of the plastic pellets is not absolutely necessary.

The suspension can also be filtered off from the solvent and then by washing, first with approx. 5% ammonia solution and then several times with distilled water. be freed from all low molecular weight organic compounds. The filter residue, as above, provides a homogeneous material after air drying. This process can also be repeated several times.

The use of, for example, gelatin, (pyrogenic) silica or starch as a colloid stabilizer can be avoided in the adsorption of silver to the inorganic particles, since the microcrystalline silver particles formed during the reduction are adsorptively bound to the surface of the inorganic particles and thus the formation of a closed silver layer on the solid is prevented. Used water-soluble auxiliary chemicals can be removed with ater W ^τ.

By varying or omitting the colloid stabilizers and the reducing agents, the particle size of the silver and thus the mobility of the resulting silver ions can be controlled in a wide range and, moreover, the use of low molecular weight aldehydes as reducing agents, which partially crosslink the gelatin, ensures very good adhesion to the Polymer can be achieved.

The process according to the invention is illustrated below by examples. Example 1:

Production of the silver colloid

1.0 g of gelatin (DAß) are distilled at 40 ° C in 100 ml of distilled water. dissolved with stirring. Then 1.0 g (5.88 mmol) of AgNO ₃ pa is added and the resulting solution is mixed with 1.0 ml (14.71 mmol) of 25% NH ₃ water.

To display the silver colloid, 258.7 mg (5.88 mmol, 330 μl) of acetaldehyde dissolved in 50 ml of distilled water are slowly added to the above solution at 40 ° C. over a period of 30 min. dripped.

Example 2:

Coating of polyurethane pellets

10 minutes after the end of the dropping according to Example 1, about 50 g of polyurethane pellets made from Tecothane TT-1085A are added and the mixture is first stirred vigorously for 2 hours at 40 ° C. and then for 3 hours at RT for coating with colloidal silver.

The silver colloid is separated off by rapid filtration through a pleated filter of a suitable pore size, the pellets are washed again with the filtrate and the pellets which are still moist are transferred to an evaporation pan. After removing excess silver colloid solution not adhering to the polymer, drying is carried out at 70 ° C. for 10 h.

Example 3:

Adsorption of colloidal silver on barium sulfate

a) In 500 ml aqua dest. 0.666 g of gelatin and then 6.66 g of AgNO _{3 are} dissolved in succession at 50 ° C. About 8.5 ml of 25% aqueous NH ₃ solution are added until the reaction is weakly alkaline.

A solution of 3.53 g of anhydrous α-D-glucose in 150 ml of distilled water is slowly added at 50 ° C with vigorous stirring. and the resulting silver colloid, when about half of the glucose solution has been added dropwise, is mixed with 333 g BaSO. After the dropwise addition has ended, the suspension is subjected to a further turbine treatment at 50 ° C. for about 2 hours and then freed of the volatile components by evaporation and drying at 70 ° C. The material is crushed in a hand mortar.

b) Procedure analogous to example 3a), but using 6.66 g of pyrogenic silica (Degussa, Aerosil 200) instead of gelatin. The particle size of the colloidal silver was in the range from 10 to 50 nm, determined by means of an SEM image.

Example 4:

Alternative adsorption of colloidal silver on barium sulfate

Procedure analogous to example 3a), but with 1.2 l of distilled water, 2 g of gelatin, 20 g of AgNO ₃ and 26 ml of 25% NH ₃ solution. A solution of 10.59 g of glucose in 400 ml of distilled water is used as the reducing agent. used and treated analogously to Example 3a) with 333 g BaSO. The suspension is then subjected to a further turbine treatment at 50 ° C. for 3 hours and kept at 70 ° C. for about 8 hours to complete the reaction. The Ag colloid absorbed at BaS0 _{4 is} filtered by filtering the suspension, which is still as warm as possible, and then washing the residue four times with distilled water. separated from the water and the constituents soluble therein (gelatin, gluconic acid, NH ₄ N0 ₃ and NH ₃ ). The drying takes place at 70 ° C. and the comminution as in example 3a).

The remaining proportion of organic material (gelatin, gluconic acid, glucose) of the material obtained according to Example 4 was determined by means of two mutually independent methods, provided that gelatin and gluconic acid have comparable solubility in water under the conditions used. By combustion analysis:

The C and H values are below the measurement tolerance of 0.3% specified by the device manufacturer, i.e. that a finished compounded polyurethane material with 20% BaSO and 0.8% Ag has a theoretical total organic residual content of theoretically a maximum of 0.182% by weight ( maximum possible lower detection limit of the device). The actual value should therefore be much lower. By thermogravimetry:

By comparing the material obtained according to Example 4 with an identically produced but not washed-out reference sample (weight loss approx. 3.2%) and pure BaS0, there is a total weight loss of at most 0.28% by weight (gelatin: 0.045% by weight) , Gluconic acid: 0.235% by weight) or better. The finished compounded polyurethane with 20% BaSO and 0.8% Ag thus has an overall organic residual fraction of <0.056% by weight (gelatin: <0.009% by weight, gluconic acid: <0.047% by weight). Thermogravimetry is preferable to combustion analysis because of the significantly higher sensitivity.

Example 5:

Determination of the antibacterial effectiveness

To determine the settability of the plastic body according to the invention with germs, five cylindrical samples of the corresponding plastic (diameter 3 mm, length 13 mm) with a composition containing Staphylococcus epidermis were incubated in a Trypcase-Soy-Broth nutrient solution at 175 ° C. The following plastic bodies were examined (number 1 is commercially available and untreated, numbers 2 and 3 are in accordance with the invention): test body 1: piece from a PU catheter from Arrow (ES 04701) test body 2: according to example 2 of the present invention test body 3: according to example 3 of the present invention.

The 5 test specimens in each case were subjected to four test series under the following conditions:

Test series 1: initial concentration of Staphylococcus epidermis 5 x 10 ⁷ CFU / ml

Test series 2: initial concentration of Staphylococcus epidermis 10 ⁸ CFU / ml

Test series 3: as test series 1, but measured after a 5-hour preincubation in physiological buffer solution at 37 ° C. Test series 4: as test series 1, the plastic bodies having been pretreated with sterile filtered natural ham at 37 ° C. for 4 hours. Table 1 shows the number of populated plastic bodies. This was determined by visual control.

Table 1

After compounding, the catheter materials show no impairment of the mechanical properties required for therapeutic purposes (roughness, homogeneity and elasticity). The process can be adapted well to changing requirements in the production process, since the antimicrobial effectiveness is retained regardless of whether the silver is introduced into the polymer material via a coating of the polyurethane pellets (example 2) or via the X-ray contrast agent (examples 3 and 4) becomes.

The plastic articles according to the invention show a significantly higher antimicrobial effectiveness with regard to adherence and biofilm formation and a significantly improved long-term behavior than previous materials, with a comparably low toxicity.

The manufacturing processes according to the invention are easy to control, inexpensive and suitable for large-scale production. In addition, a method was developed with Example 4 to remove all "auxiliary chemicals" from the inorganic contrast medium, so that certification of the method should not pose any problems.

Example 6:

Time dependence of the antimicrobial effectiveness

Catheter (the quantities are based on the finished, compounded material): 1) polyurethane catheter 20% BaSO ₄ + 0.8% Ag 1.0 cm length (example 4) 2a) Silicone catheter 25% BaSO + 1% Ag 1 cm long, 1.3 mm thick and 2 mm wide (example 4) 2b) Silicone catheter 25% BaSO ₄ + 0.33% Ag + 0.33% SiO ₂ (example 3b )

Wall pieces of silicone 1 cm long, 1 mm thick and 2 mm

Width 3) Control: ArgenTec 1 lumen catheter (Sicuris) Extr. 1/99

20% BaSO ₄ + 0.9-1% Ag sterilization: Storage in a hot air cabinet at 90 ° C for 3 hours. Previous investigations showed that the samples were sterile after this time. (Samples have largely not been germ-populated beforehand)

Germs: S. epidermidis (Ref .: Infection Suppl. 6/99) E. coli

Culture medium: Trypcase soy

Procedure:

• Samples are incubated for 8 hours in a suspension of NaCl 0.45% with 2.5% glucose with 5 x 10 germs at room temperature

• The germ suspension is then centrifuged off

• 2 x washing (2 min resuspension in physiological saline while swirling)

• Transfer the samples to sterile saline in a petri dish

• Hourly, after 6 hours, 2-hourly sampling and transfer after swirling gently in physiological saline in Trypcase Soy Medium

Incubation for 24-36 hours

• Assessment of the sterility of the sample (turbidity = end point measurement).

Results of the examinations with S. epidermidis All samples are tested 5 times (+++++) Time: Sample 1 Sample 2 a Sample 2 b Control h

0 +++++ I l I l I +++++ -H-

1 i i i i i i I I I

2 +++++ +++++ ++

3 ++++ - ++++ - M I M

4 ++++ - + - ++

5 ++ - + - ^■ ++ 6 + ++ - +++++

8 +++++

10 ^• IIII i

12 ^• III! ^■ -

16

18 - ~

+ = Bouillone cloudy after 36 hours

- = Bouillone clear after 36 hours (sterile)

Discussion:

In this investigation, a time-resolved antimicrobial effectiveness of solids could be tested. It turns out that the antimicrobial effectiveness of the silver-filled samples already exists after 6 hours and that a contaminated catheter is already sterile again even with an unphysiologically high inoculum. A lower Ag concentration as in sample 2b also leads to a positive result.

Results of the investigations with E. coli All samples are tested 5-fold (+++++) Time: Sample 1 Sample 2 a Sample 2 b Control h

0

1

2 H ~

3 ++++ -

4 ++++ - -H- +

5 ++++ -

6

8th

10 + .— + .—

12

16 - + -

18 - +.

The results for S. epidermidis are equally good even after 1, 2 and 3 weeks of elution of the silver in physiological NaCl solution and show results identical to those in Table 1.

The examination of the cytotoxicity was carried out by the company Toxikon, Bedford Mass, USA. It was shown that the samples produced are non-toxic and meet the requirements of the elution test ISO 10993.

Claims

claims 1. A method for producing an antimicrobial plastic body, comprising the molding of a preliminary product, characterized in that at least one component of the preliminary product is treated with a metal colloid before the molding. 2. The method according to claim 1, wherein the intermediate product consists of one or more polymeric materials. 3. The method according to claim 2, wherein the intermediate product consists of polyurethane. 4. The method according to any one of claims 1 to 3, wherein further additives are added to the plastic precursor in addition to the polymeric materials. 5. The method according to claim 4, wherein the additives consist of inorganic particles. 6. The method of claim 5, wherein the inorganic particles comprise barium sulfate, calcium sulfate, strontium sulfate, titanium oxide, aluminum oxide, silicon oxide, zeolites, mica, talc or kaolin. 7. The method of claim 6, wherein the inorganic particles comprise barium sulfate and / or fumed silica. 8. The method according to any one of claims 1 to 7, wherein one or more of the precursor components are treated with the colloidal metal. 9. The method according to any one of claims 4 to 7, wherein both the plastic and the inorganic particles are treated with the colloidal metal. 10. The method according to any one of claims 4 to 7, wherein the inorganic particles are treated with the metal colloid. 11. The method according to any one of claims 1 to 10, wherein the metal colloid is colloidal silver. 12. The method according to any one of claims 1 to 11, wherein the treated preliminary product is brought into the final shape by mixing, kneading, extruding, injection molding or (hot) pressing. 13. Plastic body available according to one of claims 1 to 12. 14. Plastic body according to claim 13, wherein the colloidal silver has a particle size of 10 to 50 nm. 15. Plastic body according to claim 13 or 14 in the form of a catheter.